Re: Problem with Netpoll based netdumping and NAPI

From: Hariprasad Nellitheertha
Date: Wed Apr 21 2004 - 01:04:44 EST

Hi Matt,

On Mon, Apr 19, 2004 at 12:42:54PM -0500, Matt Mackall wrote:
> [changed cc: from linux-net to netdev]
> On Mon, Apr 19, 2004 at 06:21:48PM +0530, Hariprasad Nellitheertha wrote:
> > Hi All,
> >
> > I am facing a problem while trying to network dump using LKCD. My
> > debugging so far indicates that this is due to both NAPI and NETPOLL
> > being enabled.
> >
> > I am using LKCD on the 2.6.5 kernel and both the client and server are
> > i386 boxes. The dumping machine has an e100 card. I have built the kernel
> > with both CONFIG_E100_NAPI and CONFIG_NET_POLL_CONTROLLER (and the other
> > netpoll related options) selected.
> >
> > LKCD uses netpoll for its network dump implementation. The problem we see
> > is that the network dump driver does not receive any packet from the
> > card driver and hence dumping fails. In e100_intr(), we call
> > netif_rx_schedule() if we are using the NAPI feature. netif_rx_schedule,
> > in turn, ends up adding the processing of this packet to the NET_RX_SOFTIRQ
> > softirq.
> Netpoll should be manually calling the NAPI poll function like this
> after calling the interrupt handler (in netpoll_poll()):
> /* If scheduling is stopped, tickle NAPI bits */
> if(trapped && np->dev->poll &&
> test_bit(__LINK_STATE_RX_SCHED, &np->dev->state))
> np->dev->poll(np->dev, &budget);
> Please ensure that LKCD is calling netpoll_set_trap(1) which tells it
> that packet scheduling is stopped.

This was indeed the problem. We were not calling netpoll_set_trap in LKCD.
Adding this fixed the problem. Thanks so much for your help with this.

Regards, Hari

> I've tested this path primarily with tg3 and kgdb-over-ethernet, but
> it should be functionally quite similar to e100 and lkcd.
> --
> Matt Mackall : : Linux development and consulting

Hariprasad Nellitheertha
Linux Technology Center
India Software Labs
IBM India, Bangalore
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